1. Field of the Invention
The present invention relates to a network system, a control apparatus, a router device, an access point, and a mobile terminal, which are used in a network implementing paging control.
2. Description of the Related Art
Paging control in a conventionally known mobile communication system is performed by using a control interface of a link layer provided in each mobile communication system.
However, such paging control has a problem in that paging control cannot be implemented over mobile communication systems having different link layers.
In order to overcome such a problem, IP paging control is known. In the IP paging control, when a control apparatus (paging agent) receives a packet destined for to a mobile terminal (host, mobile node), the control apparatus obtains location information of the mobile terminal (e.g., subnet prefix, IP address) by transmitting a paging notification packet to a paging area of the mobile terminal, so as to determine a transfer destination of the received packet.
The IP paging control can implement paging control in which differences between the link layers over different mobile communication systems are hidden by forming a paging area from subnet units of an IP layer.
Moreover, P-MIP technology is known, which performs paging control by means of a foreign agent (FA) representative of a plurality of FAs or by means of a paging agent managing a paging area, by extending Mobile IPv4.
However, the conventional IP paging control has a problem in that transmission load is high, because a paging notification packet is transmitted individually to all subnets constituting a paging area by using a standard unicasting method.
The conventional IP paging control also has a problem in that limited wireless resources are wastefully consumed, because, before a paging notification packet is transmitted, access routers have to transmit neighbor discovery packets based on a protocol for searching for a neighbor, such as ARP (Address Resolution Protocol) or NDP (Neighbor Discovery Protocol).
The conventional IP paging control further has a problem in that a control apparatus is congested with replies of ICMP (Internet Control Message Protocol) error packets. Because, in the case that there is no reply to the neighbor discovery packets transmitted when receiving the paging notification packet having a unicast address including a subnet prefix of an access router as a destination, the access router transmits an ICMP error packet indicating the result that the paging notification packet is unreachable to the control apparatus.
Here, the ICMP is a control protocol prepared for complementing the functions of TCP/IP, and is used for notification of various errors occurring while a TCP/IP packet is being transferred, confirmation of operation, and the like.